Fuel injection arrangement

ABSTRACT

A fuel injection arrangement, which comprises a fuel source and a fuel nozzle connected thereto, including a fuel chamber and a needle valve arrangement in connection with the fuel chamber for controlling the fuel injection and an arrangement for bringing about a force effect on the valve of the needle valve arrangement in the closing direction thereof; a fuel control arrangement by means of the different switching positions of which, the fuel flow connection is connectable between the fuel source and the fuel chamber of the fuel nozzle as well as between the fuel source and the arrangement for bringing about a force effect, in which the fuel control arrangement comprises a mechanical force unit for changing its switching positions.

This is a national stage application filed under 35 USC 371 based onInternational Application No. PCT/FI2002/00032 filed Apr. 18, 2002, andclaims priority under 35 USC 119 of Finnish Patent Application No.20011011 filed May 14, 2001.

TECHNICAL FIELD

The invention relates to a fuel injection arrangement.

BACKGROUND ART

The fuel injection has a very big influence on operation and combustionof a diesel engine. The so-called common rail fuel injection has beendeveloped in order to enhance the control of the combustion. One of thesystems of this kind, applied especially to large engines, has beendisclosed in EP 959245.

One of the factors having a particularly big influence on the operationof the engine is the successful operation and control of the injectionnozzles.

DISCLOSURE OF THE INVENTION

An objective of the invention is to provide a fuel injectionarrangement, by which the operation of the common rail injection isreliable and by which the risk of leakage of the injection nozzles tothe combustion chamber can be minimized.

The fuel injection arrangement according to the invention comprises:

-   -   a fuel source and a fuel nozzle connected thereto, which fuel        nozzle includes a fuel chamber and a needle valve arrangement in        connection with the fuel chamber for controlling the fuel        injection and an arrangement for bringing about a force effect        on the valve of the needle valve arrangement in the closing        direction thereof,    -   a fuel control arrangement, by means of the different switching        positions of which, the fuel flow connection is connectable        between the fuel source and the fuel chamber of the fuel nozzle        as well as between the fuel source and the arrangement for        bringing about a force effect, in which injection arrangement        the fuel control arrangement comprises a mechanical force unit        in order to change its switching positions.

The fuel control arrangement advantageously comprises a valve element,the position of the stem of which determines the operational state ofthe injection arrangement. There is a mechanical force unit connected tothe stem, by which the stem is displaceable between the first position,in which the valve element closes the flow connection between the fuelsource and the fuel chamber of the needle valve arrangement and connectsthe fuel chamber of the needle valve arrangement to a space allowing thelowering of its pressure, and the second position, in which there is aflow connection between the fuel source and the fuel chamber of theneedle valve arrangement. According to the invention, between the firstand second position the stem has an intermediate position, in which thefuel flow connection is connected from the fuel source to thearrangement for bringing about a force effect on the valve of the needlevalve arrangement.

The mechanical force unit comprises a stem arrangement displaceable byelectric power, which is connected to the stem of the valve arrangement.The mechanical force unit further comprises a spring arrangement orsimilar, which subjects the stem of the valve element to a force tendingto move it to a direction which opens the needle valve arrangement.

DISCLOSURE OF DRAWINGS

In the following, the invention will be described, by way of example,with reference to the accompanying drawings, in which

FIG. 1 shows schematically the fuel injection arrangement according tothe invention in the first position,

FIG. 2 shows schematically the fuel injection arrangement according tothe invention in the intermediate position, and

FIG. 3 shows schematically the fuel injection arrangement according tothe invention in the second position.

In FIG. 1, the reference numeral 1 corresponds to the fuel injectionarrangement. The arrangement comprises a common rail storage 2 as thefuel source. The fuel in the common rail storage is ready in apressurized state to be injected to the combustion chamber of the enginethrough a fuel nozzle 3. The fuel nozzle 3 includes a fuel chamber 4,from which fuel is injected to the engine cylinder, in connection withwhich the nozzle has been arranged (not shown in the Figure). The fuelnozzle also comprises a needle valve arrangement 5 for controlling thefuel injection. There is arranged, fitted with the fuel nozzle, anarrangement for bringing about a force effect 6 on the valve of theneedle valve arrangement in the closing direction thereof. Thisarrangement 6 comprises a piston unit 6′, by which the force closing theneedle valve can be directed into it.

The arrangement further comprises a fuel control arrangement 7, by whichthe fuel flow connection is connectable between the fuel source 2 andthe fuel chamber 4 of the fuel nozzle 3 as well as between the fuelsource 2 and the arrangement for bringing about the force effect 6. Withthis arrangement, between the switching on and off of the fuel feed, aforce can be directed to the needle valve arrangement in the closingdirection thereof, in which case the closure of the needle is assuredafter the injection. The solution has also other advantages, whichappear in the following description of the fuel control arrangement 7.

The control arrangement 7 comprises a valve element, the stem 8 of whichhas been arranged to move in the direction of its longitudinal axis inthe body of the valve element 14. The stem 8 and the body 14 definetogether two seat surfaces 9 and 10, which separate the three fuelspaces 11, 12 and 13 of the valve element. In the first position of thestem, the stem 8 of the valve element closes the flow connection betweenthe fuel source 2 and the needle valve arrangement 5 and connects thefuel chamber 4 of the needle valve arrangement 5 to a space allowing thelowering of its pressure 15. This situation has been represented inFIG. 1. The common rail storage 2 is connected by a duct 2′ to the fuelspace 11 of the control arrangement 7, which in this position of thestem is closed from the fuel space 12 by a seat surface 9. A connectingduct 12′ has been arranged from the fuel space 12 into the fuel chamber4 of the valve element. The fuel space 12 is still in this position ofthe stem 8, via an open seat surface 10, connected to the fuel space 13,which is connected to the piston unit space 6′. There is a furtherconnection from the piston unit space 6′ into the space 15 via duct 13″.The duct 13″ is advantageously equipped with a throttling element 13′″in order to restrict the flow.

For controlling the position of the stem 8 of the valve element amechanical force unit 16, 17 is arranged, which comprises a stemarrangement 16 displaceable by electric power, fitted to the first endof the stem 8 and a spring arrangement 17, which is fitted to the secondopposite end of the stem 8. With the interaction of the stem arrangement16 displaceable by electric power and the spring arrangement 17, thestem 8 can be placed in two different positions and in the intermediateposition thereof. The first position of the stem 8 has been shown in theFIG. 1. In this position, the feed from the common rail storage 2 isclosed and the fuel chamber 4 is in connection with the space 15 throughthe fuel spaces 12 and 13, as well as via the piston unit 6′, in orderto lower the pressure from the fuel chamber 4. This means that theneedle valve arrangement 5 is closed.

The intermediate position of the control arrangement 7, in which thefuel flow connection is connected to the arrangement for bringing aboutthe force effect 6, has been represented in FIG. 2. By means of amechanical force unit 16, such a force has been applied against theforce of the spring 17 that the stem 8 has shifted to tile positionshowed in FIG. 2. Consequently, this position is the intermediateposition of the stem before the third position, or before the first,depending on each moving direction of the stem. In the intermediateposition illustrated in FIG. 2, the stem 8 is in such a position thatboth seat surfaces 9 and 10 are open, in which case the pressure of thecommon rail storage 2 has an effect on the valve needle and to the upperside thereof by means of the piston unit 6′ as well as to the lower sidethereof, in the fuel chamber 4. This guarantees that the needle remainsclosed before the injection. In this situation, some fuel flows out ofthe system through the duct 13″, but the throttling 13′″ has beenselected to be such, that this amount is not excessive.

FIG. 3 shows a situation in which the fuel injection is in operation.Now the stem 8 is in a position, in which the seat surface 10 is closed,but the seat surface 9 is open. This means that the common rail storage2 is in connection through the fuel space 12 with the fuel chamber 4 andwhen the seat surface 10 is simultaneously closed up, the pressure mayfall in the piston unit 6′ when it is in connection with the space 15through the duct 13″. When the injection is to be halted, the stem 8 isdisplaced through the position represented in FIG. 2 into the positionillustrated in FIG. 1 assisted by the force unit 16. Among other things,this provides the reliable closure of the valve needle as a result ofthe high pressure of the common rail storage led into the piston unit6′.

The arrangement also comprises a constant pressure valve 19, by whichthe pressure acting on the piston unit 6′ is maintained at a certainlevel. By mechanically changing the position of the stem 8, thepossibility of the stem 8 to get stuck is minimized, but if the stem 8stays in an intermediate position, the needle valve arrangement 5 willclose, because the pressure of the common rail storage 2 has also avalve closing influence through the piston unit 6′. This way the leakingof the fuel from the needle valve arrangement into the engine cylinderdoes not occur. The arrangement also comprises the ducts 18 and 18′ fordischarging the fuel out of the spaces remaining between the ends of thebody and the stem.

1. A fuel injection arrangement for connection to a source of fuel underpressure, the fuel injection arrangement comprising: a fuel injectionnozzle defining a fuel chamber for receiving fuel under pressure, thefuel injection nozzle comprising a needle valve element disposed in thefuel injection nozzle for controlling injection of fuel from the fuelchamber and a force mechanism for urging the needle valve element in aclosing direction thereof, wherein the force mechanism comprises apiston unit provided with a flow connection through a drain ductequipped with a throttle element, and a fuel-control arrangement havingan inlet for connection to the source of fuel under pressure and havinga first operating state in which the fuel control arrangement isolatessaid inlet from both the fuel chamber and the piston unit, a secondoperating state in which the fuel control arrangement provides aconnection between said inlet and the fuel chamber, and an intermediatestate, between the first and second operating states, in which the fuelcontrol arrangement provides a connection between said inlet and boththe fuel chamber and the piston unit, and wherein the fuel controlarrangement comprises a mechanical force unit for selectivelytransferring the fuel control arrangement between the first and secondoperating states by way of the intermediate state.
 2. A fuel injectionarrangement according to claim 1, wherein in the first operating stateof the fuel control arrangement the fuel chamber is connected to thedrain duct.
 3. A fuel injection arrangement according to claim 1,wherein the fuel control arrangement comprises a valve member having astem and wherein the stem is movable between a first position, in whichthe fuel control arrangement is in the first operating state, and asecond position, in which the fuel control arrangement is in the secondoperating state, by way of an intermediate position, in which the fuelcontrol arrangement is in the intermediate state.
 4. A fuel injectionarrangement according to claim 3, comprising a mechanical force unitcoupled to the stem of the valve member for displacing the stem betweenthe first position and the second position.
 5. A fuel injectionarrangement according to claim 4, wherein in the first position of thestem the fuel chamber is connected to a drain outlet.
 6. A fuelinjection arrangement according to claim 4, wherein in the firstposition of the stem the fuel chamber is connected to the drain duct. 7.A fuel injection arrangement according to claim 4, wherein in theintermediate position of the stem said inlet is connected to the pistonfor exerting a force on the needle valve element.
 8. A fuel injectionarrangement according to claim 3, wherein the mechanical force unitcomprises an actuator that is connected to the stem of the valve memberand is operable by electric power.
 9. A fuel injection arrangementaccording to claim 3, wherein the mechanical force unit furthercomprises a spring that resists movement of the stem of the valve memberin a direction from the first position towards the second position.